Utility pull-back tension monitoring arrangement with sensor output compensation and method

ABSTRACT

Tension monitoring is described using a sensor which may exhibit an offset for which compensation may be provided to produce a zero voltage amplified output or to increase dynamic range. An arrangement determines whether a power reset is responsive to a battery bounce such that an initially-measured system start-up parameter can be retained. The start-up parameter is automatically saved at start-up if the power reset is responsive to a start-up from a shut-down condition. The start-up parameter may be a zero tension amplified output responsive to the sensor offset at zero tension. Protection of a tension data set is provided such that no opportunity for altering the data set is presented prior to transfer of the data set. A housing configuration forms part of an electrical power circuit for providing electrical power to an electronics package from a battery.

RELATED APPLICATION

The present application is a continuation application of applicationSer. No. 12/835,100 filed Jul. 13, 2010 now U.S. Pat. No. 8,042,407;which is a continuation application of application Ser. No. 12/506,986filed Jul. 21, 2009 and issued as U.S. Pat. No. 7,775,121 on Aug. 17,2010; which is a divisional application of application Ser. No.12/017,413 filed Jan. 22, 2008 and issued as U.S. Pat. No. 7,578,201 onAug. 25, 2009; which is a divisional application of application Ser. No.11/283,022, filed on Nov. 17, 2005 and issued as U.S. Pat. No. 7,343,816on Mar. 18, 2008; which is a divisional application of application Ser.No. 10/443,193, filed on May 22, 2003 and issued as U.S. Pat. No.6,993,981 on Feb. 7, 2006; which claims priority from U.S. ProvisionalApplication Ser. No. 60/383,023, filed on May 24, 2002; all of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates generally to the field of tension monitoringduring installation of underground utilities. As an example, the methodand apparatus of the present invention may be used in the tensionmonitoring arrangement described in U.S. Pat. No. 5,961,252 (hereinafterthe '252 patent) which is incorporated herein by reference. FIG. 3 ofthe '252 patent illustrates an installation operation in progress duringwhich a utility is pulled through a previously formed pilot bore.Tension is monitored using a tension monitoring arrangement 60. FIG. 5of the '252 patent schematically illustrates the tension monitoringarrangement used in the operation of FIG. 3.

SUMMARY OF THE INVENTION

As will be described in more detail hereinafter there is disclosedherein a system for installing an underground utility by retraction thatis applied to a leading end of the utility to draw the utility throughthe ground such that the utility is subjected to a tension force.

In one aspect of the present invention, a sensing arrangement is usedfor sensing the tension force that is applied to the leading end of theutility to produce a sensor signal. An amplifier arrangement uses thesensor signal to generate an amplified output signal. A compensationarrangement applies a compensation voltage to the amplifier arrangementfor shifting the amplified output signal.

In another aspect of the present invention, the system includes aninground tension monitoring arrangement having a processing arrangementwhich receives electrical power from a power supply in a way which maysubject the processing arrangement to a loss of power that is temporaryduring system operation, as well as a shut-down loss of power condition,either of which causes the processing arrangement to reset. The systemfurther includes a first arrangement for producing an output signal thatis responsive to a time duration of the loss of power. A secondarrangement cooperates with the processing arrangement for using theoutput signal to establish whether a particular reset is responsive to apower supply bounce condition during operation. In one feature, theprocessing arrangement is configured for saving at least one systemstart-up parameter at an initial system start-up and is furtherconfigured for re-entering a run mode responsive to establishing thatthe particular reset is responsive to the power supply contacts bouncecondition, while retaining the system start-up parameter.

In still another aspect of the present invention, the system includes asensing arrangement for inground sensing of the tension force that isapplied to the leading end of the utility to produce a sensor signalsuch that a zero tension sensed value may be offset from a zero voltage.An amplifier arrangement uses the sensor signal to generate an amplifiedoutput signal such that a zero tension amplified output is producedresponsive to the zero tension sensed value. Processing means isconfigured for measuring the amplified output signal at least in a waywhich measures the zero tension amplified output responsive to poweringon the sensing arrangement and the amplifier arrangement, and for savingthe zero tension amplified output. In one feature, the processing meansis configured for issuing a ready for calibration signal after savingthe zero tension amplified output and the system includes ingroundtransceiver means for transmitting the ready for calibration signal toan above ground location.

In yet another aspect of the present invention, a tension monitoringapparatus is provided including sensing means for inground sensing ofthe tension force that is applied to the leading end of the utility toproduce a sensor signal during the installation time period. Data meansis used at least for storing an original digital data set responsive tothe sensor signal, during the installation time period and for copyingthe original data set to a different data location to create a copieddata set after the installation time period. A user interfacearrangement, in communication with the data means, permits erasing theoriginal data set only after the original data set has been copied tothe different data location. In one feature, the data means isconfigured for creating the original data set in a way which providesfor detection of any alteration of the copied data set at the differentdata location.

In a further aspect of the present invention, a tension monitoringapparatus includes sensing means for sensing the tension force toproduce a tension signal. Electronic means is provided for using thetension signal. Battery means is provided for supplying electrical powerto the electronic means. Housing means supports the sensing means in away that exposes the sensing means to the tension force and furtherdefines an elongated chamber between a pair of opposing, first andsecond ends. The housing means being electrically conductive and a firstone of the ends being configured for receiving the tension force suchthat the tension force is transferred through the housing means to thesecond one of the ends for then transferring the tension force to theutility. The electronic means is positionable in the chamber with thebattery means such that the housing means serves as at least a portionof an electrical circuit for supplying the electrical power to theelectronic means from the battery means. In one feature, the electronicmeans is further configured for at least one of recording the tensionforce, based on the tension signal, and transmitting the tension forceto an aboveground location. In another feature, the elongated chamber isat least generally cylindrical in shape having a chamber diameter thatis defined by an interior chamber surface and the battery means includesat least one battery cell that is cylindrical in shape so as to definean outer cylindrical surface and the battery cell is received in theelongated chamber such that the outer cylindrical surface of the batterycell is supported directly against the interior chamber surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be understood by reference to the followingdetailed description taken in conjunction with the drawings brieflydescribed below.

FIG. 1 is a schematic diagram of one embodiment of the tensionmonitoring arrangement of the present invention, shown here for purposesof illustrating its highly advantageous configuration.

FIG. 2 is a flow diagram which illustrates one embodiment of a highlyadvantageous start-up and calibration procedure in accordance with thepresent invention.

FIG. 3 is another flow diagram which illustrates one embodiment of runmode in accordance with the present invention.

FIG. 4 is an partial cutaway view of one embodiment of the highlyadvantageous tension monitoring arrangement of the present invention,shown here to illustrate details of its structure.

FIG. 5 is a perspective view of a first end fitting that is used in thetension monitoring arrangement of FIG. 4, shown here to illustratedetails of its structure, particularly with respect to providing batterypower to an electronics package that is housed within the tensionmonitoring arrangement.

FIG. 6 is a perspective view of a second end fitting that is used in thetension monitoring arrangement of FIG. 4, opposite the first end fittingof FIG. 5, shown here to illustrate details of its structure, again withrespect to providing battery power to an electronics package that ishoused within the tension monitoring arrangement as well as positioningand support of strain gauges that are used to sense tension force beingapplied to a utility.

FIG. 7 is another perspective view of the second end fitting of FIG. 6,shown here to illustrate further details of its structure.

FIG. 8 is a perspective view of the end fitting of FIGS. 6 and 7 shownpositioned adjacent to the electronics package.

FIG. 9 is a diagrammatic view, in elevation, shown here to illustratethe use of the tension monitoring arrangement of the present inventionin a winching configuration.

FIG. 10 is a diagrammatic view, in elevation, shown here to illustratethe use of the present invention for monitoring tension as applied by acrane.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the figures of the present application, wherein referencenumbers of the '252 patent have been applied to like components wherepossible, attention is immediately directed to FIG. 1. This figureillustrates a portion of the arrangement of components shown by FIG. 5of the '252 patent including strain gauge arrangement 82 (within adashed box), battery 87, power supply 88 and CPU 92. Additionalcomponents are shown including a multiplexer 100, an analog to digitalconverter (A/D) 102, a digital to analog converter (D/A) 104, adifferential amplifier arrangement 106 (within a box) having (+) and (−)inputs that are connected to strain gauge arrangement 82 at P1 and P2,respectively. It is noted that component additions may not be required,in order to practice the present invention, where previously installedcomponents have unused capacity which may be pressed into service. Forexample, multiplexer 86 of FIG. 5 in the '252 patent may serve in placeof multiplexer 100 of FIG. 1 of the present application. In this regard,identity of components is not required so long as functional equivalenceis achieved in view of the teachings herein. It is noted that the plus(+) and minus (−) amplifier input markings were inadvertently reversedin FIG. 1 of the above incorporated provisional application. While thishas been corrected, along with a few typographical changes in thisdescription, it is submitted that one of ordinary skill in the art wouldimmediately reverse the markings in view of the functionally describeddifferential amplifier configuration that is clearly in use.

Continuing to refer to FIG. 1, strain gauge arrangement 82 is made up ofstrain gauges S1-S4 in an H bridge configuration. As an example, inconsidering tension monitoring, strain gauges S1 and S4 may be orientedalong the axis of pull with S2 and S3 oriented orthogonal thereto.Accordingly, S1 and S4 stretch responsive to pulling the utility beinginstalled. Voltage at P1 will decrease, while voltage at P2 willincrease. The decrease and increase in voltages at these respectiveconnections comprise inputs to differential amplifier 106 which, inturn, cooperate to provide an output responsive to tension. This tensionoutput is sent to multiplexer 100 channel 3 input on a line 110 forconversion to digital form and is selectively available to processor 92.Strain gauges S2 and S3, in the present example, being orientedorthogonally with respect to the axis of pull, are not subjected topulling tension but may be used advantageously for purposes such astemperature compensation. Of course, the present invention contemplatesthat alternative arrangements of the various strain gauges may beemployed which result in different tension orientations with respect toeach individual one of the strain gauges.

While it is sometimes desirable for strain gauge arrangement 82 toprovide a voltage output of zero volts in the absence of any pullingtensions, it should be appreciated that such a strain gauge arrangementtypically does not exhibit a zero offset. That is, the output at zeropull taken between P1 and P2 is offset from the desired zero volt value,as provided to the inputs of differential amplifier arrangement 106.Moreover, as will be seen, it may at times be desirable to provide anoffset voltage at the input of the differential amplifier arrangementfor purposes of increasing dynamic range, for example, with respect topulling force. These and other desired offset conditions are encompassedby the concept of a compensation offset signal to be provided to theinput of the differential amplifier in a way which produces a desiredoffset in the output of the differential amplifier, as describedimmediately hereinafter.

Still referring to FIG. 1, a compensation line 112 is connected fromdigital to analog converter 104 to the connection point between S3 andS4 (P2) and is thereby capable of influencing one input of thedifferential amplifier arrangement in a desired manner so as to providea compensation offset signal. In this way, a target offset value can beprovided at the input of the differential amplifier arrangement. Forexample, microprocessor 92 may provide digital data to digital to analogconverter 104 which then provides an analog voltage output that istailored to cause the differential amplifier arrangement to output avalue of zero volts despite an offset voltage at the output of thestrain gauge arrangement. Generally, in this arrangement, the (+) inputof the differential amplifier is biased at approximately one-half of thepower supply voltage.

Moreover, it should be appreciated that compensation line 112 mayreadily be used to apply compensation in a way that produces some otherdesired target offset in the output of the differential amplifier. Forinstance, the desired offset may be intended to increase dynamic range.That is, for example, where only tension monitoring is of interest, anoffset at the differential amplifier inputs may deliberately be producedwhich allows the voltage that is induced by tension in the strain gaugearrangement to produce a larger voltage swing in a known direction. As aspecific example, the (+) input of the differential amplifier may bebiased downward to a value that is less than one-half of the supplyvoltage value for this purpose. Accordingly, highly advantageous offsetcompensation has been provided.

During any pulling operation directed to installing an undergroundutility, the tension monitoring arrangement may be subjected tosignificant values of mechanical shock and/or vibration. Where battery87 is installed in a battery compartment and may be comprised of one ormore cells which are spring biased toward one another, it should beappreciated that momentary power interruptions or disconnections may beinduced by such shock and vibration. It is recognized herein that suchmomentary power interruptions may produce conditions under whichmicroprocessor 92 is reset during the drilling operation. In thisregard, system calibration with respect to pulling tension is generallyperformed at system startup under controlled conditions with one or moreselected values of tension applied to the drill string and the tensionmonitoring arrangement. It is further recognized that startup proceduresmay be initiated responsive to a battery bounce reset in the absence ofappropriate provisions. For example, a start-up calibration proceduremight be initiated which could replace valid calibration data or zerooffset with erroneous data. The apparatus and method of the presentinvention are configured for advantageously distinguishing suchmomentary power disconnections from initial power up or start upconditions, as will be described immediately hereinafter.

Continuing to refer to FIG. 1, a highly advantageous detectionarrangement 200 is illustrated within a dashed line. Detectionarrangement 200 includes resistors R1-R3, diode D1 and a capacitor C1.It is considered that one of ordinary skill in the art may readilyselect component values in view of this overall disclosure. Thisdetection arrangement serves the purpose of distinguishing betweenmomentary power interruptions and system start up conditions. To thatend, when battery 87 is connected to the system at start up, the batterywill charge C1 through R1 and the diode D1. If it is assumed that R1 isabout the same resistance value as R2, and the time constant provided bythe product R2*C1 has a value of about a few seconds, when battery 87 isremoved from the system for more than a few seconds (i.e., a shutdowncondition), R2 will discharge C1, and the voltage to multiplexer 100 viaA/D converter 102 will be proportional to (1−exp(−t/(R2*C1)), where t isthe time in seconds. In this instance, the voltage on the channel 1input of multiplexer 100 will be less that some predetermined thresholdvalue based on system parameters. On the other hand, when the batterybounces, causing a system reset, the voltage at R3 (pin 1 of multiplexer100) is about ½ of battery voltage minus one diode drop across D1 suchthat the voltage seen by the microprocessor is significantly higher thanthat voltage which is read after a system start up condition.Accordingly, when the microprocessor reads A/D 102 after a power-onreset or reset(s) due to battery bounce, it is able to distinguishbetween a just installed battery (low voltage at C1) and a reset causedby battery bounce (C1 voltage will be close to steady state voltage).

In accordance with the present invention, a startup calibrationprocedure or zero adjust offset measurement is applied only after thesystem is powered up and microprocessor 92 detects that the voltage atC1 is sufficiently low. That is, the voltage is detected before C1 isable to charge to a value above a predetermined minimum thresholdthrough R1 indicating a start-up condition. As will be seen, the methodemploys an auto-zero on startup feature as well as a tension calibrationfeature using one or more non-zero tensions applied to the tensionmonitor.

Turning to FIG. 2, a highly advantageous start up and calibration methodis generally indicated by the reference number 300. Method 300 isinitiated at power-up step 302. Step 304 then measures the output ofdifferential amplifier arrangement 106 with zero tension applied to thetension monitoring arrangement and stores the offset value. Thereafter,a “Ready for Calibration” message is transmitted in step 306 to anaboveground location which may comprise a receiver at the drill rig or atest fixture specifically directed to that purpose.

The receiver or test fixture then originates a response which may bereferred to as a calibration signal. Step 308 is performed at thetension monitoring arrangement in which the latter listens for thecalibration signal at a periodic interval. Step 310 tests for receipt ofthe calibration signal. As the system awaits the calibration signal,operation is transferred through decision step 312 which itself testsfor the expiration of an overall time out interval anticipating receiptof the calibration signal. Where the time out interval has not expired,operation returns to step 308. Steps 308, 310 and 312 are continuouslyexecuted in a loop until expiration of the time out interval. Followingexpiration of the time out interval, step 314 sends a calibration timeout message to the aboveground receiver, followed by step 316 in whichoperation is transferred into a normal run mode with the new zero offsetvalue, an implementation of which is described below.

Returning to the description of step 310, when the calibration signal isreceived, step 318 is entered in which zero tension is applied to thedrill string and tension monitoring arrangement. Step 320 then adjuststhe output of digital to analog converter 104 so as to generate thecompensation signal on line 112 to produce a target value output fromthe differential amplifier at the channel 3 input of multiplexer 100.The output of the digital to analog converter is adjusted repetitivelyuntil the target value is achieved. Thereafter, settings of the digitalto analog converter which achieved the target value are stored by step322 in nonvolatile memory. In step 324, tension applied to the tensionmonitoring arrangement by the drill string is adjusted to a nonzerovalue for calibration purposes. For example, a tension of 40,000 poundsmay be applied to the tension monitoring arrangement. With this tensionapplied, step 326 is performed wherein microprocessor 92 selects thechannel 3 input of multiplexer 100 to read the output of differentialamplifier, as converted to digital form by analog to digital converter102. In this regard, it should be appreciated that strain gauge responseis at least generally linear. Therefore, a calibration constant may beobtained using a single nonzero tension value, however, it is to beunderstood that additional nonzero tension values may readily be used.With one or more nonzero tension values in hand, step 328 determines acalibration constant k for use in determining tension based on output ofthe differential amplifier. The calibration constant being determinedas:

$k = \frac{{applied}\mspace{14mu}{tension}}{\left( {{A/D}\mspace{14mu}{{reading}@{tension}}} \right) - {offset}}$

Step 330 stores calibration constant k in nonvolatile memory. A“calibration complete” message is then transmitted, in step 322, to thereceiver at an aboveground location such as, for example, receivers R1and R2, as shown in FIG. 2 of the '252 patent, a drill rig receiver or atest fixture receiver.

FIG. 3 illustrates one potential implementation of the run mode,generally indicated by the reference number 400 and entered at step 402.In step 404, a measurement interval or period is initiated for theduration of which tension is monitored. In step 406, a tension value ismeasured by microprocessor 92 using the voltage value obtained from thechannel 3 input of multiplexer 100 and the stored zero offset value.Step 408 may transmit this tension value, for example, to an abovegroundreceiver for use in displaying the tension value to an operator,comprising a display which is presented essentially in real-time. Step410 determines whether the tension value just measured is a new maximumtension for the measurement interval which is currently underway. If thetension value is a new maximum, step 412 saves that value in a data setcorresponding to the current measurement interval in a way which isdescribed in further detail hereinafter.

If the tension value just measured is not a new maximum tension valuefor the interval underway, step 414 tests whether the measurementinterval has concluded. If the measurement interval is ongoing, theprocess repeats, beginning with step 406. If, on the other hand, thecurrent measurement interval has concluded, step 416 determines whetherthe overall installation operation has concluded. In the event that theinstallation operation is continuing, the process resumes by initiatinga new measurement interval at step 404 and determining a maximum tensionvalue for the new interval, as described above. If step 416 determinesthat the installation has concluded, step 418 initiates an uploadprocedure in which the data set produced by step 412 is copied toanother location in a protected manner. Following the upload procedureof step 418, the data set may be erased in step 420 using step 422. Stopstep 424 concludes the run mode. It should be appreciated that thisinstallation procedure is advantageous at least for the reason that evena long installation run produces a data set of relatively limited size,since maximum interval values are stored. Moreover, the system mayreadily present an overall maximum value that is selected from theinterval maximums. Of course, the data set may be presented in anynumber of suitable manners.

It should be appreciated that run mode procedure 400 does not afford anopportunity to alter or erase the data set prior to upload. Moreover, itis desirable to protect the data set from unauthorized alteration. Inthis regard, any number of techniques currently available or yet to bedeveloped, may be employed even during step 412, which creates the dataset and adds new values to it to prevent and/or detect data alteration.For example, the data set may be subjected to cyclic redundancy checking(CRC) wherein even the modification of a single bit is readily detected.Moreover, proprietary formats may be used or developed which may includeencryption, either currently available or yet to be developed, thatessentially eliminates the possibility of data alteration. In additionto proprietary formats, proprietary devices may be used to initiallystore the data set and/or to receive the upload of the data set. It isrecognized herein that access to the data set is not particularly ofconcern so long as alteration of the data set is prevented.

Turning now to FIG. 4, a tension monitoring arrangement produced inaccordance with the present invention is generally indicated by thereference number 500. Arrangement 500 includes a housing 502 having atransmitter arrangement 504 positioned therein. Housing 502 defines aninnermost passage having a diameter which is sized to receive a pair ofbatteries 506 that are connected in series. In this particular example,D cell batteries are used, however any suitable type of battery may beused. Power is supplied to transmitter 504 at the end of one of thebatteries nearest the transmitter using a spring biasing and electricalcontact arrangement 508 which forms part of the transmitter arrangement,as will be seen in further detail in a subsequent figure. Opposing endsof the housing are closed using a pair of plug arrangements indicated bythe reference numbers 510 and 512, each of which defines a pulling eye514.

Referring to FIG. 5 in conjunction with FIG. 4, plugs 510 and 512 aresimilar in defining a through hole 516 (FIG. 5) that is configured forreceiving a pin 520 (FIG. 4) through cooperating holes defined inhousing 502 so as to hold the plugs in position. O-ring seals 522 (FIG.5) are used to seal the plugs against housing 502.

Plug 512 includes a spring contact arrangement 523 made up of a housingcontact spring 524 and an inner, battery contact spring 526 both ofwhich are best viewed in FIG. 5. Housing 502 defines a recess that isconfigured for receiving housing contact spring 524 so as to form anelectrical contact between the housing contact spring and housing 502.Battery contact spring 526 places a resilient bias against a nearest oneof batteries 506 and forms an electrical contact with its end terminal.At the same time, battery contact spring 526 is electrically connectedto plug 512.

Referring to FIGS. 4, 6 and 7, plug 510 is illustrated including itshighly advantageous configuration with respect to delivering power totransmitter arrangement 504 from batteries 506. To that end, plug 510includes a fastener receptacle 530 which may be configured for receivinga threaded fastener 532 or any suitable type of fastener. An electricalconnection such as, for example, a wire 534 provides an electricalconnection to transmitter arrangement 504. Any number of different formsof electrical connection may be employed as an alternative between plug514 and the transmitter including, for example, spring biasing. A recess536 is formed in the sidewall of plug 510 for receiving a coil spring538 (FIG. 6). When plug 510 is installed in housing 502, spring 538 iscaptured between the plug and housing so as to form an electricalconnection therebetween. It should be appreciated that additionalrecesses 536 and springs 538 may readily be used to enhance electricalconnectivity.

In view of the features described above, electrical power is suppliedfrom the battery using housing 502 in cooperation with end plugs 510 and512 in a highly advantageous manner. In particular, this configuration,wherein the housing is used as an electrical path, optimizes thestrength of the housing by avoiding the need for a separate batterycompartment which would result in reduced thickness of the housing walland by allowing for greater battery diameter and thereby increased powercapacity.

FIG. 8 illustrates plug 510 positioned adjacent to transmitter 504 tofurther illustrate details of its structure including spring biasing andelectrical contact arrangement 508.

It should be appreciated that the highly advantageous tension monitoringarrangement of the present invention may be used in systems other thatin conjunction with being pulled using a drill rig and drill string.FIG. 9 diagrammatically illustrates one such alternative systemgenerally indicated by the reference number 650. System 650 includes awinch 652 arranged for pulling a winch cable 654. The latter is attachedto tension monitoring arrangement 500 in a way which transfers winchingtension to a cable extension 656 that is attached to a pulling object658. This attachment may be accomplished, for example, using a Kellum'sgrip, as is known in the art. Pulling object 658 may comprise anysuitable elongated member including an electrical power cable or pipe.The objective of the task may be, for example, to pull the elongatedmember through a pathway, shown in phantom using a dashed line, that isdefined, for example, by a conduit or raceway either underground,aboveground, in a building or otherwise. Upon completion of theinstallation, the tension data set can be downloaded as described above.If desired, tension monitoring arrangement 500 may transmit anelectromagnetic signal 672 which may include, for example, real timetension values. Signal 672 may be received by an antenna 674 of aportable receiver 676. The latter may include any suitable form of adisplay 678 for illustrating the tension value. Moreover, aural and/orvisual warnings may be provided, if a maximum tension is about to beexceeded.

Attention is now directed to FIG. 10 for purposes of further describingthe broad range of tension monitoring tasks to which the tensionmonitoring arrangement of the present invention is well-suited. Inparticular, a crane 700 is diagrammatically illustrated having a liftingcable 702 wherein tension monitoring arrangement 500 is installed so asto be subjected to all lifting forces that are applied to a hook 704.Again, tension data can be downloaded at the conclusion of a particulartask. If desired, a receiver 706 may be located in a cab 708 of thecrane for receiving transmitted data 672 from tension monitoringarrangement 500 so as to provide a crane operator (not shown) a realtime display 712 of lifting force.

Since the system and apparatus of the present invention disclosed hereinmay be provided in a variety of different configurations and theassociated method may be practiced in a variety of different ways, itshould be understood that the present invention may be embodied in manyother specific ways without departing from the spirit or scope of theinvention. For example, it is to be understood that the describedapparatus and methods, are not limited to use in tension monitoringconfigurations, may be practiced in many other alternative andequivalent forms relating, for example, to offset compensation,resolving battery bounce conditions, as well as related resetconsiderations, data set protection and the use of a housing for powersupply purposes with attendant advantages. Therefore, the presentexamples and methods are to be considered as illustrative and notrestrictive, and the invention is not to be limited to the details givenherein, but may be modified within the scope of the appended claims.

What is claimed is:
 1. In a system for installing an underground utilityby retraction that is applied to a leading end of the utility to drawthe utility through the ground such that the utility is subjected to atension force, an apparatus comprising: a sensor for sensing the tensionforce that is applied to the leading end of the utility to produce asensor signal; an amplifier to generate an amplified output signal basedon the sensor signal; and a compensator to apply an offset signal tosaid amplifier to shift said amplified output signal such that theamplifier at least produces a target value as the amplified outputsignal based on the sensor signal at a zero value of the tension force.2. The apparatus of claim 1 wherein said sensor is a strain gauge thatproduces a nonzero offset voltage as the sensor signal when said tensionforce is equal to zero and wherein said compensator is configured tocause said amplified output signal to be at least approximately equal tozero volts as the target value when the tension force is at leastapproximately equal to zero.
 3. The apparatus of claim 1 wherein saidoffset signal is configured for shifting the amplified output signal toincrease an available voltage swing of the amplifier responsive to saidtension force to increase a dynamic range of the amplified outputsignal.
 4. The apparatus of claim 1 wherein said compensator includes adigital to analog converter to generate the offset signal.
 5. Theapparatus of claim 4 wherein the compensator includes a processorconfigured to track the amplified output signal responsive to the offsetsignal and provide a digital drive signal to the digital to analogconverter to selectively control the offset signal.
 6. The apparatus ofclaim 5 wherein said processor is configured for repetitively adjustingsaid digital drive signal to obtain the target value of said amplifiedoutput signal.
 7. The apparatus of claim 4 wherein said processor isfurther configured to save a specific value of the digital drive signalwhich achieved said target value of the amplified output.
 8. Theapparatus of claim 1 wherein the amplifier is a differential amplifier.9. The apparatus of claim 8 wherein the differential amplifier includesa non-inverting input that receives the offset signal.
 10. In a systemfor installing an underground utility by retraction that is applied to aleading end of the utility to draw the utility through the ground suchthat the utility is subjected to a tension force, a method comprising:sensing the tension force that is applied to the leading end of theutility to produce a sensor signal; generating an output signal that isresponsive to said tension force and based on the sensor signal; andshifting said output signal at least to produce a target value as theoutput signal based on the sensor signal at a zero value of the tensionforce.
 11. The method of claim 10 wherein a nonzero offset voltage isproduced as the sensor signal responsive to a zero value of said tensionforce prior to said shifting and wherein said shifting causes the outputsignal target value to be at least approximately equal to zero volts atzero tension.
 12. The method of claim 11 wherein shifting includesapplying a compensation signal that shifts the output signal in a waywhich increases an available voltage swing in the output signalresponsive to said tension force to increase a dynamic range of theoutput signal.
 13. The method of claim 12 wherein applying saidcompensation signal includes (i) producing the output signal as ananalog output, (ii) digitally tracking the analog output, (iii)generating a digital drive signal responsive to the analog output, (iv)converting the digital drive signal to an analog drive signal, and (v)adjusting the analog output responsive to the analog drive signal. 14.The method of claim 13 including repetitively performing (i)-(v) tomaintain the target value.
 15. The method of claim 14 further includingsaving a specific value of the digital drive signal which achieved thetarget value.
 16. The method of claim 10 wherein generating includesamplifying the output signal.